Thermocouple Circuit

[JKellyNPFD]

I've decided to make my own digital thermometer as a side project. I want to use a type K thermocouple as the sensing element. I'm using a PIC16F777 micro with an LCD output. I've got code (using picbasic pro) that will display the ADC to the LCD. I'm looking for information that will help me linearize the Thermocouple. I'm assuming it will be a mix of ciruitry and code. If anyone has any app notes, or can point me in the right direction it would be greatly appreciated.

Thanks

 

[itsmoked]

More importantly have you measured your isothermal terminal block with a non-T/C sensor so you can negate that error voltage?

Look at the tech notes on Omega's website.

Go with a lookup table.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[JKellyNPFD]

I think i'm going to use an NTC thermistor to measure the iso thermal block. Or probably an easier method would be to use a digital temperature sensor since it is linear and i can wire it directly to the uProcessor

 

[itsmoked]

The easiest are the linear temp sensors by National Semi. 10mV/degree.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Madcow]

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en012021

This should help.

 

[MacGyverS2000]

You've had two posts now about temp sensors... what is this for?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[JKellyNPFD]

I've been a controls engineer for about 6 years now using PLC's like Allen Bradley and Semens to control temperature within a specific environment. In my effort to understand the internal workings better (and to become more fluent with my electronics) I’ve decided to build a simple digital thermometer using various methods.

Thanks Madcow, I'll start with the app note you provided.

 

[jimkirk]

What range of temperature do you want to measure? Solid state sensors are great, but operate over a range typical of semiconductors, something like -50 to 150 degrees C. If that's sufficient, that's the way to go.

 

[bioe007]

I have used this for TC amplification with good results,

http://www.analog.com/en/prod/0,2877,AD595,00.html

has built in CJC, as long as you keep the TC termination as close to the IC pins you're golden.

 

[itsmoked]

Welcome to the fora bioe007!

I agree that chip works well JKelly.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[450x]

Be aware of common mode voltage errors. I think this chip likes to have a grounded T/C